[Press Release] Professor Jeonghun Kwak Laboratory Develops High Performance Thermoelectric Energy Conversion Technology

January 26, 2024l Hit 90
Seoul National University's College of Engineering (Dean: Yoosuk Hong) announced that Professor Jeonghun Kwak from the Department of Electrical and Computer Engineering and Professor Keehoon Kang from the Department of Materials Science and Engineering, along with the research team led by Professor Sunghyun Kim from the Department of Carbon Convergence Engineering at Wonkwang University (co-authored by Juhyung Park and Jaegyu Jang), have developed an organic semiconductor thermoelectric device with the world’s highest performance.
Thermoelectric generation is a semiconductor-based technology that enables the conversion of waste heat to electrical energy using temperature differences. Currently bulk inorganic thermoelectric semiconductors have been preferred due to their high performance, their field of application has been limited due to their toxic, heavy, rigid characteristics, and poor economic efficiency for low temperature applications. On the other hand, thermoelectric generators based on organic thin film semiconductors are light and thin, and can be manufactured to be flexible & stretchable, able to form conformal contact to curved surfaces. Also, since they are environmentally friendly, they can form direct contact with human skin, potentially appliable to a variety of fields. However, their commercialization has been challenging due to their poor thermoelectric effectiveness compared to their inorganic counterparts.
In order to enhance the performance of organic thermoelectric generators, charge concentration of polymers and density of states must be precisely engineered by methods such as molecular doping. However, due to the decrease in the polymer’s crystallinity during the doping process, the thermoelectric effect is weakened, and fundamental understanding of heat & charge transport mechanisms of doped conductive polymers with irregular structures of crystalline and non-crystalline regions is very difficult. Such problems have been a major bottleneck for improving the performance of thermoelectric generators.
The joint research team addressed this problem by using a consecutive oxidization-reduction doping, based on trifflic acid to control the density of states for a widely used conductive polymer, PEDOT:PSS. Based on this method, they succeeded in controlling charge concentrations without losing the crystallinity of the PEDOT:PSS thin film, achieving a record high thermoelectric performance of power factor 534.5 μW/mK2. Through charge transport modeling, they also found the theoretical limit for the thermoelectric performance obtainable from their system, and focused on the aspect that even without degradation in crystallinity, experimental results could not reach the theoretical limit. Researcher Juhyung Park, the first author of the corresponding paper conducted analysis on the difference between experimental results and the theoretical limits based on various points of views, including the Hall effect, magnetoconductance, density functional theory. Through his analysis, he clarified, “The change in tie-chain structures of nanometer(nm) scale that connect the polymer’s crystalline regions interrupt the penetration of charge, limiting the performance of thermoelectric generators.”
The co-corresponding author, professor Jeonghun Kwak stated, “This study presents a direction for development of high performance organic thermoelectric devices. The study also enables fundamental knowledge of charge transport in polymers, and we expect it to contribute to the development of various organic semiconductor-based electronic devices including thermoelectric generators.”

The results of this research were published on the 18th of January online on one of the most prestigious journals in the field of materials, nano technology and science, “Advanced Science”. The research was conducted through support from the Korea Research Foundation's Outstanding Young Researcher Support Program, the Creative Challenge Research Infrastructure Support Program, the Regional University Excellent Scientist Program, and the Information Technology Future Talent Education and Research Team's BK21four program.

(From the Left) SNU Professor Jeonghun Kwak, Wonkwang University Professor Sunghyun Kim, SNU Professor Keehoon Kang, SNU Ph. D Juhyung Park, Wonkwang University Ph. D Jaegyu Jang


Source: http://www.energy-news.co.kr / https://ece.snu.ac.kr/ece/news?md=v&bbsidx=54257

Translated by: Jiyong Yoo, English Editor of the Department of Electrical and Computer Engineering, cyoo7@snu.ac.kr